Electric rotational tools, which are constructed so that the driving of an electric motor is initiated by operating a driving switch, work such as the tightening of screws etc. is accomplished by driving a rotational tool such as a driver bit or the like by means of the driving of this electric motor, the load torque that is generated in the rotational tool when the work is completed is detected by a torque detection means, and, when the detected load torque reaches a torque value that has been preset by a combination of a torque adjustment spring and a cam, this state is detected by a torque setting automatic stopping means, and the driving of the rotational tool is automatically stopped, have been known in the past as electric rotational tools such as electric drivers or the like that are driven by an electric motor.
For example, drivers, which are constructed so that when a strong opposing load is applied to the driver bit during the tightening of screws or the like, this state in which a specified torque value has been reached is detected by a clutch mechanism that is operated by a preset tightening torque, and the clutch mechanism is operated so that the connection between the output shaft of the electric motor and the driver bit is temporarily broken, have been proposed and put into practical use as electric drivers or the like. Furthermore, electric drivers, which are constructed so that when the clutch mechanism is operated, this state is detected by a limit switch or the like, and the driving of the electric motor is stopped, have also been in practical use (Japanese Patent Application Publication (Kokoku) No. 60-13798).
Furthermore, an automatic power cutting device for an electric rotational tool, which is constructed so that the operation of the clutch mechanism is detected by a magnet piece and a magnetism detecting element (Hall element), and the driving of the electric motor is stopped by cutting the power to the electric motor, has also been proposed (Japanese Patent Application Publication (Kokoku) No. 60-3960).
Furthermore, when a switching circuit is installed in a power supply circuit of electric drivers or the like which have a driver bit that is rotationally driven by an electric motor, and if a specified tightening torque is reached as the completion of the screw tightening approaches, then the load current that flows to the power supply circuit when the electric motor is driven increases to an excessive load current that exceeds a specified value. Accordingly, electric drivers or the like equipped with an automatic power cutting device, which is constructed so that the above-described state is detected and the supply of a driving current to the electric motor is cut off, after which the supply of a driving current to the electric motor is restored when a fixed period of time has elapsed, and which is further constructed so that a switching mechanism is installed in the armature circuit of the electric motor, and the armature circuit of the electric motor is short-circuited when the switching circuit cuts off the supply of a driving current to the electric motor, thus instantaneously stopping the electric motor by regenerative braking, have also been proposed (Japanese Patent Application Publication (Kokoku) No. 57-43389). In the above, since the above-described switching circuit is in an OFF state for only a fixed period of time, this circuit also has a function in which the switching circuit automatically returns to an ON state at the timing of the next screw tightening operation, so that the electric motor is driven, thus allowing immediate initiation of the next screw tightening operation.
Furthermore, in an electric rotational tool of this type, an external AC power supply (commercial power supply) is generally used in the driving control of the electric motor. In this case, a control unit equipped with an AC/DC power conversion function and a torque control function, etc. is used in order to obtain the external AC power supply as a suitable power supply output for the driving of an electric motor. In cases where an ordinary compact DC motor is used as the electric motor, this control unit is constructed as a unit that is independent of the electric rotational tool, and is connected between the AC power supply and electric rotational tool so that driving control of the electric motor is accomplished.
Nowadays, furthermore, brushless motors, which are superior as DC motors in terms of characteristics such as non-contact operation, prevention of noise, high torque and compact size, high-speed rotation and long useful life, etc. and which offer the advantage of maintenance-free operation, have been proposed for use as electric motors in electric rotational tools, and they have seen in practical application. In the case of driving control of such brushless motors, unlike the case of the DC motors, a driving circuit that generates a rotating magnetic field is required. Furthermore, such a driving circuit can be constructed by means of a magnetic pole sensor (a Hall element is generally used) which detects the position of the magnetic poles with respect to the magnet rotor, a driving coil which is excited so that a rotational force in a fixed direction is imparted in accordance with the positions of the rotor magnetic poles, and a special IC circuit which controls the driving of the magnetic pole sensor and driving coil.
The driving circuit constructed in this way can be accommodated as a compact circuit structure together with circuits that have a torque control function, etc. inside the grip portion casing of the electric rotational tool. Accordingly, in cases where a brushless motor is used, a control unit having a structure that is independent of the electric rotational tool such as that described above is unnecessary; and only an AC/DC converter is required, and the driving circuit, etc. can be installed in the electric rotational tool as a simplified structure, so that handling can be simplified.
Furthermore, as a means of simplifying handling in electric rotational tools of this type, push operating systems and lever operating systems have been employed as driving switches for starting the driving of the electric motor. The former push operating system is a system which is constructed as follows: when the operator grips the electric rotational tool and presses the rotational tool, such as a driver bit, etc., that protrudes from the tip end portion against the work object, such as a screw, etc., the rotational tool undergoes elastic displacement in the axial direction, so that a driving switch, such as a micro-switch, etc., is switched ON using this displacement, thus connecting the electric motor to a specified power supply, so that the driving of the electric motor is initiated. On the other hand, the latter lever operating system is constructed as follows: when the operator grips the electric rotational tool and causes the rotational tool such as a driver bit, etc. that protrudes from the tip end portion to contact the work object, such as a screw, etc., the operator arbitrarily presses and displaces a switch lever that is installed on the grip portion of the electric rotational tool, so that a driving switch such as a micro-switch, etc. is switched ON utilizing this displacement, thus connecting the electric motor to a specified power supply so that driving of the electric motor is initiated.
In conventional electric rotational tools, as described above, a micro-switch, etc. is used as the driving switch that initiates driving of the electric motor. As a result, sparks, etc. are generated in the switch contact points at the time of operation. This not only causes wear of the contact points, but also results in the problem of various types of deleterious effects on surrounding electronic parts, electronic equipment and electronic circuits, etc. Accordingly, such a mechanical switch structure not only suffers from limits in terms of achieving a compact size and an increase in the useful life, but also places numerous restrictions on the achievement of a compact size of the electric rotational tool as a whole in terms of the structure and layout.
Furthermore, driving switches in conventional electric rotational tools have a structure that employs either a push operating system or a lever operating system, so that in cases where it is desired, for example, to change from a push operating system to a lever operating system, or vice-versa, in accordance with changes in the nature of the work involved, etc., it is necessary to prepare in advance electric rotational tools having driving switch systems with the above-described two different types of operating systems. Accordingly, if driving switches with the two different types of operating systems are installed in a single electric rotational tool, and the tool is constructed so that one or the other operating system can be selected and used as required, then the range of use of the electric rotational tool can be increased, so that an electric rotational tool with much more convenient handling can be obtained.
Accordingly, the present inventor, as a result of diligent research and the structure of numerous prototypes, confirmed the following: with the use of a combination of a magnet and a magnetic sensor, attaching the magnet to the shaft part that supports the rotational tool or to a switch lever installed in the grip portion of the electric rotational tool, connecting the magnetic sensor to the power circuit of the electric motor, disposing this sensor in the displacement position of the magnet, and operating the rotational tool by pushing (i.e., using a push operating system) or operating the lever by pushing (i.e., using a lever operating system), so that the magnet is caused to approach the magnetic sensor, the magnetic sensor will sense the magnetism and switch the power circuit ON, so that the electric motor can be rotationally driven in a simple manner.
In this case, it was confirmed that if a Hall element is used as the magnetic sensor in the driving switch of the above-described structure, the power circuit can also be made extremely small and compact by way of using an IC circuit, so that a driving switch that allows the use of both the push operating system and lever operating system can easily be installed in a single electric rotational tool. Especially in cases where a brushless motor is used as the electric motor, the driving switch and the electric motor driving control circuit can both be accommodated in a compact manner inside the grip portion casing of the electric rotational tool, so that handling is convenient.
Furthermore, in cases where a driving switch with two different types of operating systems is thus installed, the efficiency of the work can be increased and the safety of the work can also be improved by constructing the tool so that switching which allows selective use of either operating system is possible. Furthermore, by applying the above-described conventional torque detection means and torque-set automatic stopping means when the work is completed, it is possible to achieve appropriate tightening work of screws, etc. and to stop the driving of the electric motor, so that a transition to the waiting state for the next operation can be made quickly and smoothly.
Accordingly, the object of the present invention is to provide an electric rotational tool driving switch system in which driving control by means of a desired push operating system or lever operating system can be selectively performed in accordance with the content of the work when the electric rotational tool is used, an appropriate tightening work of screws, etc. can be always performed efficiently, and handling of the tool can be simplified and safety can be sufficiently improved.